Wireless communication systems are often used where it is preferable not to create a wired link to each communicating station. Wireless communication systems may be used, for example, to communicate between rooms in building.
When a wireless communication system uses infrared (IR) signals as a means for communicating, the distance between two communicating stations is limited. Limiting factors include communication speed and whether the system is diffused or directional. In addition, when IR (infrared) communicating stations are located in different rooms, they may not be able to directly communicate with each other, because IR signals can not propagate through walls. Connectivity between areas that are separated, by walls, for example, may be achieved by using signal regeneration.
Bridges or routers may also be used for transferring IR signals between areas. A bridge or router is a network layer solution. A bridge or router first desirably validates a received frame using information in the frame. The bridge or router then decides whether to retransmit and forward the frame based on the receipt and content of this information. Different criteria and different routing algorithms for forwarding a frame are known to those skilled in the art. This decision making process results in bridges or routers delaying a frame before retransmitting the frame. Another possible source of delay in a bridge or router in retransmitting a signal from one room to another is the time to convert a signal from an IR MAC protocol to a wired MAC protocol and then back to an IR MAC protocol.
Analog or digital repeaters may also be used for IR signal regeneration. A repeater is a physical layer solution that does not implement a routing protocol nor include its associated delays. However, commonly repeaters simply retransmit a received signal without validating the signal before retransmission. This may result in the regeneration of invalid signals.
A wireless communication system 100 having a common wiring infrastructure 105 topology is shown in FIG. 1. Repeaters 112, 122, 132, 142 (generally designated "R") are connected to the common wiring infrastructure 105. A first room 110, a second room 120, a third room 130, and a fourth room 140 are separated by walls 107. A source wire less station 118 may communicate with a destination wireless station 148 by transmitting a wireless signal 116 to the repeater 112 in the first room 110. This transmission may be, for example, an IR signal. The repeater 112 then transmits the received wireless signal 116 onto the common wiring infrastructure 105. From common wiring infrastructure 105, signal 116 may be distributed to repeater 122 in Room 2, repeater 132 in Room 3 and repeater 142 in Room 4. When repeater 142 in Room 4 receives the retransmitted signal from the common wiring infrastructure 105, wireless signal 146 may be transmitted to destination 148.
Noise and unwanted signals are often present in wireless communication systems. For example, in an IR wireless communication system, thermal noise, sunlight, IR remote control devices, and light from lamps may be sources of IR noise. When the lamp 114 in FIG. 1 is turned on, the IR radiation generated by the lamp 114 may be a source of noise received by the repeater 112.
When a noise source, such as light from the lamp 114, for example, is turned on, the repeater 112 may receive the wireless signal 116 from the source wireless station 118 plus noise from the lamp 114. The noise may cause the repeater 112 to receive a false signal. A conventional physical layer repeater may retransmit the false signal, without checking for undesired signal components, onto the common wiring infrastructure 105. This may result in repeater 122 retransmitting a false signal 126 into the second room 120, repeater 132 retransmitting a false signal 136 into the third room 130, and repeater 142 retransmitting a false signal 146 into the fourth room 140 and to the destination wireless station 148.
Retransmission of a false signal by repeater 112 may inhibit communication of true signals across the common wiring infrastructure 105 between wireless stations 128, 138, 148 in rooms without noise sources. A possible disadvantage of a common wiring infrastructure 105 topology is the cost of the wiring infrastructure. A possible advantage of having a common wiring infrastructure 105 topology is having connectivity between N rooms with only N repeaters.
A wireless communication system 200, having a point-to-point topology is shown in FIG. 2. A repeater 212 in a first room 210 is connected to a repeater 232 in a third room 230 by a wiring 234 through a wall 207. Repeaters 233, 242 are similarly connected between the third room 230 and the fourth room 240. Repeaters 243, 222 are similarly connected between the fourth room 240 and the second room 220.
A source wireless station 218 may communicate with a destination wireless station 248 by transmitting a wireless signal 216 to the repeater 212 in the first room 210. The repeater 212 transmits (i.e., retransmits) the received signal to the repeater 232 in the third room 230 through the wiring 234. The repeater 232 transmits (i.e., retransmits) the received signal by a wireless transmission 236 to the repeater 233. Repeater 233 transmits (i.e., retransmits) the received signal to the repeater 242 which transmits (i.e., retransmits) the signal using a wireless signal 246 to the destination wireless station 248.
A light source such as a lamp 214 may generate noise as described above with reference to lamp 114 in FIG. 1. When a noise source, such as light from the lamp 214, for example, is turned on, an false signal may propagate from repeater 212 to repeater 232. From repeater 232 it may propagate to wireless station 238 and repeater 233, and so on to repeaters 242, 243, 222 and wireless stations 228, 248 in the second room 220 and fourth room 240.
Retransmission of a false signal by repeater 112 may inhibit communication of valid signals between wireless stations 228, 238, 248 in rooms without noise sources. A possible advantage of a point-to-point topology is that a common wiring infrastructure may not be required. A possible disadvantage of a point-to-point topology is that 2*(N-1) repeaters may be required for connectivity between N rooms.
A possible problem when using conventional physical layer repeaters that transmit and receive wireless signals on a single channel is self-distortion. The problem of self-distortion will be described with reference to FIG. 3. Self-distortion may occur due to multiple path reception in a wireless communication system 300.
A source wireless station 318 in a first room 310 may communicate with a destination wireless station 328 in a second room 320 using a repeater 312. The wireless station 318 transmits a wireless signal. The wireless signal following a first signal path 316 is received by the repeater 312. The repeater 312 retransmits the received signal to the repeater 313 which retransmits the signal into room 320. The retransmitted signal following a second signal path 326 is received by the destination wireless station 328. The wireless signal transmitted by the wireless station 318 may additionally follow a third signal path 317. The signal along signal path 317 may reach the destination wireless station 328 through an opening 322 in the wall 307 as shown in FIG. 3. The signal following path 317 may collide with the signal following path 326 from the repeater 313 and may result in a false signal reaching destination wireless station 328. The signals following paths 326 and 317 may collide rather than coincide because of path length delay differences. It is also possible for a similar collision of signals to occur at the repeater 332 in the second room 320.
The self-distortion described above may occur because at least two copies of the same signal are present simultaneously at a single destination because one or more copies of the signal is regenerated and repeated at the physical layer.